Gas separation is important in many industries and can typically be accomplished by flowing a mixture of gases over an adsorbent that preferentially adsorbs a more readily adsorbed component relative to a less readily adsorbed component of the mixture. One of the more important types of gas separation technology is swing adsorption, such as pressure swing adsorption (PSA). PSA processes rely on the fact that under pressure gases tend to be adsorbed within the pore structure of the microporous adsorbent materials or within the free volume of a polymeric material. The higher the pressure, the greater the amount of targeted gas component will be adsorbed. When the pressure is reduced, the adsorbed targeted component is released, or desorbed. PSA processes can be used to separate gases of a gas mixture because different gases tend to fill the micropore or free volume of the adsorbent to different extents.
Another important gas separation technique is temperature swing adsorption (TSA). TSA processes also rely on the fact that under pressure gases tend to be adsorbed within the pore structure of the microporous adsorbent materials or within the free volume of a polymeric material. When the temperature of the adsorbent is increased, the adsorbed gas is released, or desorbed. By cyclically swinging the temperature of adsorbent beds, TSA processes can be used to separate gases in a mixture when used with an adsorbent that is selective for one or more of the components in a gas mixture.
Various methods of supplying heat to the adsorbent for the regeneration cycle have been proposed. These include microwave energy (U.S. Pat. No. 4,312,641), installation of electrical heaters inside the packed adsorbent bed of the adsorber (U.S. Pat. No. 4,269,611) and direct application of electric current to the adsorber for electrodesorption (U.S. Pat. No. 4,094,652). However, many of the conventional TSA processes have cycle times significantly long, often as long as 12 hours, which reduces the overall adsorption and processing capacity of the system.
TSA, as conventionally practiced, has several disadvantages. For example, in directly heated TSA processes, a hot fluid is typically flowed through the adsorption bed to raise the adsorbent temperature. The greater the temperature rise, the more fluid is needed. The desorbed impurities thus end up dispersed in a large volume of heating fluid, and the large amount of heat that is used to raise the adsorbent temperature is often not recoverable. In some cases, the heat is not recovered because many directly heated TSA systems are operated with long adsorption times (days) and much shorter regeneration times. Also, the occasional and gradual adsorption and regeneration cycles give rise to concentration and flow variations in downstream equipment that can be difficult to manage in an otherwise steady state process plant. Improper or inadequate regeneration of the adsorption beds can also significantly impact the overall purity of the product streams from the adsorption process. Heat management and the cyclic nature of the TSA processes also affect the overall system capacity and product purities.
Thus, there is a need in the art for temperature swing adsorption processes that can overcome at least some of these problems as well as having faster cycle times, leading to higher system capacities, while maintaining or improving the final product stream purity, especially with regard to temperature swing adsorption processes.